Documentary reveals the science behind turtle mother calls

In the new BBC documentary Parenthood, baby turtles see sunlight for the first time and crawl towards their singing mothers

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The hatchlings of the giant Amazon River turtle (Podocnemis expansa) in Guaporé, southern Brazil, have been waiting for exactly the right conditions to break free, Sir David Attenborough’s voiceover tells viewers in the new BBC series Parenthood.

He explains that once it rains, the sand becomes soft enough for the tiny turtles to dig themselves out from their nest 1m (3.3ft) below the surface. If there’s too little rain, the layer of sand above them will be too sun-hardened to break through. Too much rain and they could drown.